1. Field of the Invention
The present invention relates to a fire detector for sensing a fire by detecting a smoke caused by the fire.
2. Description of Related Art
According to an earlier development, a smoke-detecting type of the fire detector which senses a fire by detecting a smoke caused by the fire by using a light emitting element and a light detecting element is often attached to one member having a disk shape so that the light emitting element is placed at a certain angle with respect to the light detecting element, for example as described in Japanese Patent Application No. Tokukai-Hei 8-166347.
However, in case that a fire detector having such a structure identified above is miniaturized, it is difficult to prepare an enough smoke detecting area because it is inevitable to shorten a distance in a radial direction, and then a distance between the light emitting element and the light detecting element becomes shorter.
Contrarily, a fire detector as described in Japanese Patent Application No. Tokukou-Sho 57-22157, has a structure where an axis of the light emitting element are approximately perpendicular to that of the light detecting element in a height direction. It is possible to miniaturize the fire detector in the radial director by sacrificing the height, that is, a thickness of the detector because of the structure thereof.
However, in case that the fire is miniaturized in the radial direction, it is necessary to prepare the smoke detecting area as large as possible.
Alternatively, the distance between the light emitting element and a wall of the smoke chamber storing the light emitting element necessarily becomes shorter by miniaturizing the detector. A reflected light generated by a reflection of a light from the light emitting element on the wall or the like is not reduced. Such a reflected light is detected by the light detecting element as a noise light, and a problem including a decrease of an S/N ratio occurs.
Further, each part of the fire detector may be located accurately in assembly process in order to stabilize the performance of the fire detector. However, regarding the assembly of the smoke chamber, when the detector is miniaturized, a space for a screw nut used frequently in a fire detector according to an earlier development, must be needed. Therefore, it is not preferred because of the restriction of the space.